1. Field of the Invention
The present invention relates to a facility control system comprising an apparatus controller that controls an operation of a facility apparatus, a first-layer computer that executes a first-layer program for issuing an apparatus operating command for the facility apparatus to the apparatus controller that the first-layer computer is assigned to and for managing an operation result of the facility apparatus transmitted from the apparatus controller, a second-layer computer that executes a second-layer program for issuing a task command to the first-layer computer in order to cause the facility apparatus required to process a task request to be operated in accordance with the task request which is a request for an operation that is to be accomplished by operating the facility apparatus, and for managing a result of a task that is related to the task request based on the operation result of the facility apparatus transmitted from the first-layer computer, as well as to a facility control method using such a facility control system.
2. Description of the Related Art
Facility control systems such as one described above are used, for example, in a distribution facility that includes, as facility apparatuses, an automated warehouse having stacker cranes each of which transfers an article between an article storage rack and itself, sorting carriages for transporting articles along a predetermined track, storing-and-retrieving conveyers for storing and retrieving articles between carrying-in-and-out locations for the stacker cranes in the automated warehouse and carrying-in-and-out locations for the sorting carriages, and receiving-and-delivering conveyers for receiving and delivering articles between the carrying-in-and-out locations for the sorting carriages and article shipment locations, etc.
The facility control system in such distribution facility includes computers (first-layer computers) each of which runs a computer program (first-layer program) that issues apparatus operating commands for the facility apparatuses to the apparatus controllers which control operations of the facility apparatuses and that manages the operation results of the facility apparatuses transmitted from the apparatus controllers, and a computer (second-layer computer) which runs a computer program (second-layer program) that issues task commands to the first-layer computers and that manages the operation results of the facility apparatuses transmitted from the first-layer computers.
The second-layer computer issues a task command in accordance with a task request based on a storing-and-retrieving schedule, etc., to the first-layer computers that are assigned to the facility apparatuses that are required to operate in order to process the task command. And the first-layer computer issues apparatus operating commands for the facility apparatuses based on the task command, to the apparatus controllers that the first-layer computer is assigned to. (See, for example, JP Application Publication No. H09-136705 (Patent Document 1)).
In the facility control system of the distribution facility disclosed in Patent Document 1, the first-layer computers (control devices for the automated warehouse) issue the apparatus operating commands to the apparatus controllers each of which individually controls the operation of each apparatus, such as a stacker crane, based on the task command from the second-layer computer (facility controller) which manages the entire facility. And the first-layer computers are configured to manage article management information which is information that specifies the articles stored in the article storage unit based on information on operation results from the apparatus controllers, such that storage position information given uniquely to each of a plurality of article storage units of the article storage rack is associated with identifying information unique to each article stored in the storage position. This article management information is outputted to the second-layer computer through a communication line. And the second-layer computer is configured to perform inventory management based on the storage position information and on the identifying information unique to each article, by creating rack data (inventory data) by associating the storage position information with the unique identifying information.
Because the facility control system for the distribution facility disclosed in the above-described Patent Document 1 is configured in this manner, for example, if an abnormal condition occurs in the second-layer computer and even if normal operation of the second-layer computer is subsequently restored in such a manner that the data etc. that were stored before the occurrence of an abnormal condition were initialized, the rack data (inventory data) for inventory management can be reconstructed based on the article management information stored in the first-layer computers, which makes it possible to restore the system quickly.
However, while the inventory data can be recovered easily with such a configuration after an abnormal condition occurs in the second-layer computer, the facility apparatuses which one of the first-layer computers is assigned to can not continue to operate if an abnormal condition occurs in the first-layer computer.
In the field of information processing systems using a computer, non-stop computer systems have been implemented to avoid the problem that it becomes impossible to continue a process that a program executed by the computer has been performing if an abnormal condition occurs in the computer executing the program for performing the process. A non-stop computer system includes a computer under operation (referred to as an operational computer) and a computer (referred to as a standby computer) whose sole purpose is to provide the functions of the operational computer in substitution therefor. And when an abnormal condition occurs in an operational computer, a failover is performed from the operational computer to the standby computer, in which the standby computer takes over the process performed by the program that had been executed by the operational computer in which the abnormal condition occurred. Thus, the process is continued to be performed without interrupting or stopping the information processing system. Such a non-stop computer system is called a high availability cluster.
When employing a high availability cluster, a mutually monitoring mechanism called Heartbeat, etc. is provided between the operational computer and the standby computer to detect an abnormal condition. However, in a high availability cluster, because, among other reasons, the mutually monitoring mechanism may misinterpret a momentary disruption of the network communication between the operational computer and the standby computer as an abnormal condition occurring in the operational computer, there is a possibility that a condition (so-called split-brain syndrome) may occur in which the standby computer is automatically activated by the system despite the fact that the operational computer is functioning normally.
In a facility control system such as one disclosed in Patent Document 1 described above, when a high availability cluster is introduced, in which the first-layer computers are the operational computers, there would be two first-layer computers that execute the same first-layer program if and when the above-described split-brain syndrome occurs because, for example, a momentary disruption of the network communication between the operational computer and the standby computer is misinterpreted as an abnormal condition occurring in the operational computer. Then, there is a possibility that a plurality of apparatus operating commands may be issued to the apparatus controller assigned to one facility apparatus. For example, if an advance command and a retreat command are issued simultaneously, as the plurality of apparatus operating commands, to the apparatus controller assigned to a stacker crane, there is a possibility that it may become impossible for the apparatus controller to determine what operation it should cause the stacker crane to perform. In such a case, the apparatus controller issues a command for stopping the operation in order to protect the facility apparatus, which leads to a lowering of the operation efficiency of the facility apparatus. For this reason, there has been a need, in the field of facility control systems, for a non-stop computer system that can reliably prevent occurrences of the split-brain syndrome and thus, can reduce a lowering of the operation efficiency of the facility apparatuses. In addition, in a high availability cluster, it is necessary to provide, for a given operational computer, a standby computer whose sole purpose is to substitute for the operational computer, which lead to an increase in the overall cost for the facility.